Differentials of the type used in automotive drivelines generally include a planetary gearset supported within a differential casing to facilitate relative rotation (i.e., speed differentiation) between a pair of output shafts. The planetary gearset typically includes helical side gears fixed to the end of the output shafts, which are meshed with paired sets of helical pinion gears. Each pair of pinion gears is disposed in pinion bores formed in the differential casing. Since the pinion bores are parallel to the rotary axis of the differential casing, the pinion gears rotate on axes parallel to the common axis of the output shafts and the side gears. This type of differential is known as a parallel gear type differential. In response to speed differentiation between the output shafts, the torque transmitted through meshed engagement of the side gears and pinion gears generates thrust forces. These thrust forces are exerted against the wall surface of the gear pockets and other thrust surfaces within the differential casing by the gear components to frictionally limit speed differentiation and proportion torque between the output shafts.
In order to reduce friction and provide wear protection between the pinion gears and other contacting surfaces of the differential system, various lubrication methods have been developed. One such method, as disclosed in U.S. Pat. No. 5,310,389, employs radial lubrication orifices disposed in the differential casing. The radial lubrication orifices are formed radially outward from the pinion gear meshing sections. Lubrication oil is then introduced through the radial orifices of the differential casing to the pinion gears to provide lubrication. However, due to the size of the lubrication holes, this method may not provide sufficient lubricant flow to the pinion gears. Alternatively, another lubrication method, as disclosed in U.S. Pat. No. 5,711,737, employs a plurality of lubrication holes formed in an end of the differential casing to introduce lubrication oil into the differential casing. Each lubrication hole is positioned so that its center is positioned near the pinion gear meshing point. In operation, lubrication oil is introduced through the lubrication hole and into the meshing portion of the pinion gears due to the gear pumping effect of the pinion gears. However, due to the restriction of hole size and position, it is expected that this method may not provide an optimal lubrication system.
Accordingly, there exists a need in the relevant art to provide a lubrication system for a helical gear differential capable of maximizing the gear pumping effect for improved wear protection and reduced friction of the differential system. Furthermore, there exists a need in the relevant art to provide a simplified and cost effective method of manufacturing differentials.